SPD light valves have been known for more than seventy years for the modulation of light. Such light valves have been proposed for use in numerous applications during that time including, e.g., alphanumeric displays and television displays, filters for lamps, cameras, optical fibers and displays, and windows, sunroofs, sunvisors, eyeglasses, goggles, mirrors and the like to control the amount of light passing therethrough or reflected therefrom as the case may be. Examples of windows include, without limitation, architectural windows for commercial buildings, greenhouses and residences, windows for automotive vehicles, boats, trains, planes and spacecraft, windows for doors including peepholes, and windows for appliances such as ovens and refrigerators including compartments thereof. Light valves of the type described herein are also known as suspended particle devices or SPDs.
As used herein, the term light valve describes a cell formed of two walls that are spaced apart by a small distance, with at least one wall being transparent. The walls have electrodes thereon, usually in the form of transparent, electrically conductive coatings. The cell contains a light-modulating element (sometimes herein referred to as an activatable material) which may, without limitation, be either a liquid suspension of particles or a plastic film in which droplets of a liquid suspension of particles are distributed.
The liquid suspension (sometimes herein referred to as a liquid light valve suspension or as a light valve suspension) comprises small particles suspended in a liquid suspending medium. In the absence of an applied electrical field, the particles in the liquid suspension assume random positions due to Brownian movement. Hence, a beam of light passing into the cell is reflected, transmitted or absorbed depending upon the cell structure, the nature and concentration of the particles and the energy content of the light. The light valve is thus relatively dark in the OFF state. However, when an electric field is applied through the liquid light valve suspension in the light valve, the particles become aligned and for many suspensions most of the light can pass through the cell. The light valve is thus relatively transparent in the ON state.
For many applications it is preferable for the activatable material, i.e., the light modulating element, to be a plastic film rather than a liquid suspension. For example, in a light valve used as a variable light transmission window, a plastic film in which droplets of liquid suspension are distributed is preferable to a liquid suspension alone because hydrostatic pressure effects, e.g., bulging associated with a high column of light suspension, can be avoided through use of a film and the risk of possible leakage can also be avoided. Another advantage of using a plastic film is that, in a plastic film, the particles are generally present only within very small droplets and, hence, do not noticeably agglomerate when the film is repeatedly activated with a voltage.
A light valve film (also sometimes herein referred to as an SPD film) as that term is used herein, means a film or sheet, or more than one thereof comprising a suspension of particles used or intended for use in an SPD light valve. Such light valve film shall comprise either (a) a suspension of particles dispersed throughout a continuous liquid phase enclosed within one or more rigid or flexible solid films or sheets, or (b) a discontinuous phase of a liquid comprising dispersed particles, such discontinuous phase being dispersed throughout a continuous phase of a rigid or flexible solid film or sheet. The light valve film or laminates comprising the light valve film may also comprise one or more additional layers such as, without limitation, a film, coating or sheet or combination thereof, which may provide the light valve film with (1) scratch resistance, (2) protection from ultraviolet radiation, (3) reflection of infrared energy, and/or (4) electrical conductivity for transmitting an applied electric or magnetic field to the activatable material.
U.S. Pat. No. 5,409,734 exemplifies a type of non cross-linked light valve film that is made by phase separation from a homogeneous solution. Light valve films made by cross-linking emulsions are also known. The methods of the present invention are specifically directed to the use of the latter type of film, i.e., formed by cross-linking emulsions, and to the laminated films produced thereby. See, for example, U.S. Pat. Nos. 5,463,491 and 5,463,492, both of which are assigned to the assignee of the present invention. Various types of SPD emulsions, and methods of curing the same, are described in U.S. Pat. Nos. 6,301,040 and 6,416,827, and in pending U.S. patent application Ser. No. 10/465,489, all of which are assigned to the assignee to the present invention. Such films and variations thereof may be cured through cross-linking brought about by exposing the films to (1) ultraviolet radiation, (2) electron beams and/or (3) heat. All of the references cited in this application, including patents, are incorporated herein by reference.
In general usage to “laminate” usually means (1) to separate or split into thin layers, (2) to form into a thin metal plate, (3) to construct by placing one layer upon another or (4) to cover or overlay with thin layers. (see, e.g., The Random House Dictionary of the English Language, 1967 edition). In preparing laminated products for use as or in conventional glass windows, definitions (3) and (4) above are applicable. For architectural and windshield glass applications, the lamination process generally involves bonding a plastic interlayer in between two lites (sheets) of flat or curved glass, with the goal of producing a clear unit of shatter-resistant glass.
However, as used herein in relation to SPD films, i.e., in connection with the present invention, the terms laminating, to laminate or the act of lamination refer to the combination as a unit an SPD film with (1) one or more plastic hot melt adhesive sheets or films and/or (2) with one or more glass or plastic sheets for the purpose(s), without limitation thereto, of protecting and/or strengthening the SPD film, any of the purposes mentioned hereinbefore, and/or making it easier to install where intended for use.
A variety of liquid light valve suspensions are well known in the art and such suspensions are readily formulated according to techniques well-known to one of ordinary skill therein. The term liquid light valve suspension, as noted above, when used herein means a liquid suspending medium in which a plurality of small particles are dispersed. The liquid suspending medium comprises one or more non-aqueous, electrically resistive liquids in which there is preferably dissolved at least one type of polymeric stabilizer which acts to reduce the tendency of the particles to agglomerate and to keep them dispersed and in suspension.
Liquid light valve suspensions useful in the present invention may include any of the so-called prior art liquid suspending media previously proposed for use in light valves for suspending the particles. Liquid suspending media known in the art which are useful herein include, but are not limited to, the liquid suspending media disclosed in U.S. Pat. Nos. 4,247,175, 4,407,565, 4,772,103, 5,409,734, 5,461,506, and 5,463,492, the disclosures of which, as noted above, are incorporated herein by reference. In general one or both of the suspending medium or the polymeric stabilizer typically dissolved therein is chosen so as to maintain the suspended particles in gravitational equilibrium.
The polymeric stabilizer, when employed, can be a single type of solid polymer that bonds to the surface of the particles, but which also dissolves in the non-aqueous liquid(s) which comprise the liquid suspending medium. Alternatively, there may be two or more solid polymeric stabilizers serving as a polymeric stabilizer system. For example, the particles can be coated with a first type of solid polymeric stabilizer such as nitrocellulose which, when dissolved, provides a plain surface coating for the particles, together with one or more additional types of solid polymeric stabilizer that, when dissolved, bond to or associate with the first type of solid polymeric stabilizer and also dissolve in the liquid suspending medium to provide dispersion and steric protection for the particles. Alternately, liquid polymeric stabilizers may also be used to advantage, especially in SPD light valve films, as described for example in U.S. Pat. No. 5,463,492.
Inorganic and organic particles may be used in a light valve suspension, and such particles may be either light absorbing or light reflecting in the visible portion of the electromagnetic spectrum.
Conventional SPD light valves have generally employed particles of colloidal size. As used herein the term colloidal means that the particles generally have a largest dimension averaging 1 micron or less. Preferably, most polyhalide or non-polyhalide types of particles used or intended for use in an SPD light valve suspension will have a largest dimension which averages 0.3 micron or less and more preferably averages less than one-half of the wavelength of blue light, i.e., less than 2000 Angstroms, to keep light scatter extremely low.